ATF2 background/simulation Meeting

International phone/webex meeting

Background simulation in the Shintake monitor, Marc Verderi (LLR - Ecole polytechnique) , Hayg Guler

First, Marc briefly reported the progress and issues to be discussed here.

We would like to study the background in Shintake monitor. We have two simulation tools, i.e. (1) BDSIM for transportation of beam with detailed optics and (2) our own simulation program for our detector based on GEANT4, where the BDSIM is also based on GEANT4. We would install the detector as an object in BDSIM.

What we need are detailed description of beam line with beam characteristics and mechanical description of Shintake monitor detector. Also, we would like to know what have been done for the Shintake monitor background simulation by Tokyo university group.

We discussed as follows;

Q : Do you need BDSIM, since you may need a lot of works for two programs?
I think that first priority must be a direct simulation of your detector and dump such as an actual photon detector and signal/backgroud discrimination.

A : It is not complicated to use BDSIM since both are based on GEANT4 and our experiences. More difficult one is implementation of mechanical details. Especially, it is difficult to include beam line in own program. So, it is natural work with BDSIM.

A/Q : OK, I see. For ILC-IR study, a beam line for +/- 10m around IP has been taken account in the simulation (Geant) . In general, it is difficult to simulate real beam since we donot know it.

A : With respect to distribution of beam, first we must assume it as a flat-tail beam .

Q : What beam line must be simulated at ATF2 ?

A : Relevant line is from QF1 to dump.

Q : What is realistic condition of beam at present?

A : You had better use the design with large beta optics.

C : Oroku simulated the background 2 year ago, there are presentations.

Q : Did you simulate neutron background ?

A : No. However, Suehara simulated neutrons, too. He showed background-hits v.s. timing to reach the detector in his Dr. thesis (Japanese) , where the fast peak is electro-magnetic component and the slow peak is due to neutrons. Some results will be published in a NIM paper. He also simulated background at five different positions around the dump and the upstream including a place where the Shintake monitor detector was installed.

Q: Are neutrons discriminated by timing ?

A : Yes, the timing is very useful.

Q : What is effect of neutrons in CsI (Tl) ?

A : Since neutrons are mainly from dump, they do not depend on beam optics. So, their effect must be very small in measurement of beam size.

Q : How much is the ADC gate for CsI (Tl) signals ?

A : It is a 500nsec ADC gate.

Q : There may be prompt neutrons. How fast are neutrons ?

A : Plastic bricks can help to reduce prompt neutrons < 500ns .

Q : Which components of background are come from dump?

C : In the simulation studies, aperture, alignment effect are the most important in the beam line.

Q : What is missing information for your studies?

A : It is an exact shape of magnets .

A : Andrea (LAPP) has the detailed information.

Q : What is a goal of simulation study and plan of beam test ?

A : We would like to know if BDSIM reproduces the background at ATF2? If so, it is very useful to estimate background at CLIC and ILC.

Q : What is a plan for measurements?

A : We are making several modules which are similar to previous ones, which will be sent to KEK, November. We would like to put them close to the beam line and read out signals at the same time with Shintake monitor. We will prepare EPICS readout for syncronization with DAQ and Shintake monitor data .

Q : Do you need a dedicated beam time ?

A : No. It is parasitic with Shintake monitor group.

Q : Can simulation results help for beam studies ?

A : Yes, we think. In next meeting, we will present some results.

A : The most preferable date is 7th October.

A : If possible, we would like to have Skype/phone meeting with Shintake monitor group in addition.

KEK site meeting

Progress of Shintake monitor work, Masahiro OROKU (The University of Tokyo)

Oroku reported un-resolved issue on the gain slow variation of detector during bean studies.